Gear tooth crowning arrangement

ABSTRACT

A parallel axis gear configuration constructed in accordance to one example of the present disclosure can include a first gear having a first gear tooth that includes a lead crowning across a face width thereof. The lead crowning can include (i) a first lead crown defined from a centerline to a transition point and (ii) a second lead crown defined from the transition point to a first end point. The lead crowning can include a drop-off magnitude that is greater at the second lead crown than the first lead crown.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/US2015/049411 filed on Sep. 10, 2015, which claims the benefit ofU.S. Provisional Patent Application No. 62/058,785 filed on Oct. 2,2014, U.S. Provisional Patent Application No. 62/096,009 filed on Dec.23, 2014 and U.S. Provisional Patent Application No. 62/216,685 filed onSep. 10, 2015. The disclosures of the above applications areincorporated herein by reference.

FIELD

The present disclosure relates generally to parallel-axis gears and morespecifically, to a gear crowning arrangement.

BACKGROUND

Gear trains that require torque sharing among multiple pinions may befound in the automotive industry such as in differentials andtransmissions. Limited-slip differentials which use parallel-axisgearing rely on gear meshing events, and the friction thereof, to createthe desired friction and torque bias. Gear alignment however is looselycontrolled by the fit and clearance involved between the housing andgears. These misalignments, when combined with the high torque loads,can cause less than optimal gear meshing events. Historically, thefluctuation within these meshing events can cause undesirable noise.

SUMMARY

A parallel axis gear configuration constructed in accordance to oneexample of the present disclosure can include a first gear having afirst gear tooth that includes a lead crowning across a face widththereof. The lead crowning can include (i) a first lead crown definedfrom a centerline to a transition point and (ii) a second lead crowndefined from the transition point to a first end point. The leadcrowning can include a drop-off magnitude that is greater at the secondlead crown than the first lead crown.

According to additional features, the parallel axis gear configurationcan further include a second gear that is in meshed relationship withthe first gear. The first and second gears can be helical gears. Theparallel axis gear configuration can further include a parallel axisdifferential that houses the first and second gears. The first gear caninclude a chemical vapor deposit coating thereon. The chemical vapordeposit can be BALINIT® C Star coating.

A parallel axis gear configuration constructed in accordance toadditional features of the present disclosure can include a first gearhaving a first gear tooth that includes a lead crowning across a facewidth thereof. The lead crowning can include (i) a first lead crowndefined from a centerline to a transition point and (ii) a second leadcrown defined from the transition point to a first end point. The firstand second lead crowns can have distinct magnitudes across the facewidth.

According to additional features, the second lead crown can include adrop-off magnitude that is greater at the second lead crown than thefirst lead crown. In one configuration, the first lead crown is zero.The parallel axis gear configuration can further include a second gearthat is in meshed relationship with the first gear. The first and secondgears can be helical gears. The parallel axis gear configuration canadditionally include a parallel axis differential that houses the firstand second gears. The first gear can include a chemical vapor depositcoating thereon. The chemical vapor deposit can be BALINIT® C Starcoating.

A parallel axis gear configuration constructed in accordance toadditional features of the present disclosure can include a first gearand a second gear received in a housing in a meshed relationship. Thefirst gear can include a first gear tooth that includes a first geartooth lead crowning across a face width thereof. The first gear toothlead crowning can include (i) a first lead crown defined from acenterline to a transition point and (ii) a second lead crown definedfrom the transition point to a first end point. The first gear toothlead crowning includes a drop-off magnitude that is greater at thesecond lead crown than the first lead crown. The second gear can have asecond gear tooth that includes a second gear tooth lead crowning acrossa face width thereof. The second gear tooth lead crowning can include(i) a first lead crown defined from a centerline to a transition pointand (ii) a second lead crown defined from the transition point to afirst end point. The second gear tooth lead crowning includes a drop-offmagnitude that is greater at the second lead crown than the first leadcrown. The second lead crowns of the respective first and second geartooth lead crowns align with each other providing load intensities thatinhibit micro-welding between the gears and the housing.

According to other features, the parallel axis differential can housethe first and second gears. The first and second gears can both includea chemical vapor deposit coating thereon. The chemical vapor deposit canbe BALINIT® C Star coating. The first and second gears can be helicalgears. In one configuration, the first lead crown of at least one of thefirst and second gear tooth lead crowning is non-zero.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is an exploded view of a parallel axis differential that canincorporate pinion gears according to one example of the presentdisclosure;

FIG. 2 is a perspective view of a pinion gear according to one exampleof prior art;

FIG. 3 is a side view of the pinion gear of FIG. 2;

FIG. 4 is an exploded view of a first and second pinion gear and a firstand second side gear used in the parallel axis differential of FIG. 1;

FIG. 5 is a side view of an exemplary meshing event for correspondingpinion gears according to one example of prior art;

FIG. 6 is a side view of a pair of meshing pinion gears having areas ofscuffing and deformation according to one example of prior art; and

FIG. 7 is a lead inspection profile of the pinion gear of FIG. 2;

FIG. 8 is a lead inspection profile of a pinion gear having leadcrowning constructed in accordance to one example of the presentdisclosure;

FIG. 9 is a lead inspection profile of a pinion gear having leadcrowning constructed in accordance to a second example of the presentdisclosure;

FIG. 10 is a lead inspection profile of a pinion gear having leadcrowning constructed in accordance to a third example of the presentdisclosure;

FIG. 11 is a lead inspection profile of the pinion gear shown in FIG. 9identifying additional features according to the present disclosure;

FIG. 12 is a lead inspection profile of a the pinion gear of FIG. 11 andidentifying a crowning tolerance band according to one example of thepresent disclosure;

FIG. 13 is a load intensity distribution of a pair of mating piniongears according to prior art; and

FIG. 14 is a load intensity distribution of a pair of mating piniongears constructed in accordance to one example of the presentdisclosure;

DETAILED DESCRIPTION

Reference will now be made in detail to examples of the presentdisclosure. It will be understood that the following examples are notintended to limit the disclosure. On the contrary, the instantdisclosure is intended to cover alternatives, modifications andequivalents, which may be included within the spirit and scope of thedisclosure. For example, while the following discussion is directedtoward crowning of meshed pinion gears, the same principles can beapplied to other meshed gears such as side gears in a differential.

With initial reference to FIGS. 1-4, a parallel axis differentialconstructed in accordance to one example of prior art is shown andgenerally identified at reference numeral 10. The parallel axisdifferential 10 can include one or more side gears 12, a plurality ofpinion gears 14, a differential case 20, a first cover 22, a secondcover 24 and a plurality of fasteners 28. The pinion gears 14 arehelical pinion gears. A gear train 30 can comprise one or more sidegears 12 and a plurality of pinion gears 14. During operation, theplurality of pinion gears 14 may engage the two side gears 12. The sidegears 12 may transmit torque from the respective pinion gears 14 to anoutput such as axle shafts (not shown). Each side gear 12 may have anaxis of rotation and an inner axially aligned opening 34 through whichan axle shaft may connect to the side gear 12 via a splinedinterconnection. Both side gears 12 may comprise helical teeth 36configured to rotatably mesh with corresponding helical teeth 40disposed on the pinion gears 14.

With specific reference to FIG. 3, the pinion gear 14 can include anaxial lead 42. The pinion gear 14 can include a first zone 44, a secondzone 46 and a third zone 48. The second zone 46 can be centrally locatedon the pinion gear 14. The first and third zones 44 and 48 can belocated at opposite ends of the pinion gear 14. The pinion gear 14includes crowning in the lengthwise direction. The average crowningamount is referred to as C_(β). The average crown is defined within thesecond zone 46. As will become appreciated by the discussion herein, thefirst zone 44 and the third zone 48 on a pinion gear constructedaccording to the present disclosure will have a drop-off defined inlength and magnitude.

FIGS. 5 and 6 illustrate a pair of meshed pinion gears 14 according toprior art. The respective teeth 40 of the meshed pinion gears 14 engageat an interface area 50. In some examples, as illustrated in FIG. 6, thepinion gears 14 may develop scuffing 52 and/or plastic deformation 54thereon during use.

As will become appreciated from the following discussion, the presentdisclosure is directed toward a gear tooth crowning arrangement on thepinion gears 40. The gear tooth crowning arrangement disclosed hereinpermits more consistent gear meshing events which reduce the noise,vibration and handling (NVH) level of the parallel axis differential 10.Moreover, the present disclosure can be shown to inhibit end-loading ofthe gear train 30 and compensate for any misalignments.

Turning now to FIG. 7, a baseline lead profile according to one exampleof prior art is shown and generally identified at reference 70. A facewidth 72 is horizontal or linear along the lead profile 70. No crowningis provided on the lead profile 70.

FIG. 8 illustrates a lead profile 80 having a face width 82 thatincludes a first lead crown 84 and a second lead crown 86 in accordanceto the present teachings. The first lead crown 84 is defined from acenterline 88 to a transition point 90. The second lead crown 86 isdefined from the transition point 90 to a first end point 92. In theexample shown in FIG. 8, the first lead crown 84 can be zero. Explaineddifferently, the first lead crown 84 can have no crowning. The secondlead crown 86 can have a drop-off. The drop-off can correspond to anarea of reduced gear teeth contact with a mating gear (having a similarlead crown drop-off). It will be appreciated in light of the disclosurethat the drop-off can be located in one or both of the first and thirdzones 44, 48 (FIG. 3). The lead profile 80 can be similar between thecenterline 88 and a second end point 94. In such a configuration, whileonly one end may be meshed with a corresponding pinion gear, having asimilar lead crown on both ends of the pinion gear can help withassembly as the gear may be installed into the differential case 20 witheither end first.

FIG. 9 illustrates a lead profile 100 having a face width 102 thatincludes a first lead crown 104 and a second lead crown 106. The firstlead crown 104 is defined from a centerline 108 to a transition point110. The second lead crown 106 is defined from the transition point 110to a first end point 112. In the example shown in FIG. 9, the first leadcrown 104 can be non-zero (as compared with the first lead crown 84shown in FIG. 8). The lead profile 100 can be similar between thecenterline 108 and a second end point 114. In such a configuration,while only one end may be meshed with a corresponding pinion gear,having a similar lead crown on both ends of the pinion gear can helpwith assembly as the gear may be installed into the differential case 20with either end first.

FIG. 10 illustrates a lead profile 120 having a face width 122 thatincludes a first lead crown 124. The first lead crown 124 is definedfrom a centerline 128 to a first end point 132. In the example shown inFIG. 10, the first lead crown 124 can be non-zero (as compared with thefirst lead crown 84 shown in FIG. 8). In the example shown in FIG. 10,the first lead crown 124 can be continuous from the centerline 128 tothe end point 132. Explained further, the first lead crown 124 can besimilar to the first lead crown 104 described in FIG. 9 however, thefirst lead crown 124 can continue to the first end point 132 without adefined transition. The lead profile 120 can be similar between thecenterline 128 and a second end point 134. In such a configuration,while only one end may be meshed with a corresponding pinion gear,having a similar lead crown on both ends of the pinion gear can helpwith assembly as the gear may be installed into the differential case 20with either end first. It is appreciated however that while the leadprofile 120 is shown having both ends of the pinion crowned (such as toassist with assembly), the pinion gear 14 may be constructed as havingonly one end with a lead crown.

With reference now to FIGS. 11 and 12, additional features of thepresent disclosure will be described. FIG. 11 shows features of the leadprofile 80 (FIG. 8), the lead profile 100 (FIG. 9) and the lead profile120 (FIG. 10) together. A drop-off magnitude M is identified between thefirst lead crown 124 and the second lead crown 106. In one example, thedrop-off magnitude M can be greater than a distance 150 between afoundation line 152 and a centerline 108, 128. In one example, thedrop-off magnitude M can be a multiple of 1.5 greater than a distance150. Other configurations are contemplated. A drop-off distance L isidentified between the transition points 90, 110 and the first endpoints 92, 112. The drop-off distance L can be determined based on agiven application. FIG. 12 illustrates an exemplary crowning toleranceband 170 having an upper tolerance 172 and a lower tolerance 174. Thecrowning tolerance band 170 identifies an area that the lead profile canoccupy while still providing the reduced NVH levels in a given geartrain.

FIG. 13 illustrates a load intensity distribution 200 for a pinion geardisposed in a parallel axis differential according to prior art.Notably, an active face width shows increased load intensities 202 and204 in meshed areas consistent with a meshed interface area 50 (FIGS. 5and 6). The increased load intensities 202 and 204 produce unfavorableNVH. FIG. 14 illustrates a load intensity distribution 210 for a piniongear having a lead crowning according to one of the examples of thepresent disclosure and disposed in a parallel axis differential.Notably, an active face width shows reduced load intensities 212 and 214in meshed areas consistent with a meshed interface area 50. The reducedload intensities 212 and 214 provide improved NVH characteristics. Thereduced load intensities avoids micro-welds and subsequent breaking ofthose micro-welds causing NVH chatter. The micro-welds can occur inprior art examples between the pinion teeth 40 and the housing 20.

According to other examples of the present disclosure, a chemical vapordeposit coating may be additionally or alternatively applied to thepinion gears 14 that can be shown to provide improved NVH qualities. Onesuch product is a chemical vapor deposit coating marketed by OerlikonBalzers of Liechtenstein. One example is BALINIT® C Star coatingmarketed by Oerlikon Balzers. The chemical vapor deposit coating canreduce friction and/or pressure between the pinion gears 14 and thehousing. In this regard, the coating can reduce the propensity of themicro-welds from forming between the pinion gears 14 and the housing 20and the resulting stick-slip action that would otherwise cause noise. Inprior art examples, high pressure, lack of sufficient lubricant, andsimilarity of material properties such as hardness, alloy content, andsurface finish are characteristics that can encourage micro-welds. Thechemical vapor deposit coating, such as identified above, separates andprotects the substrate materials from contacting each other in thisoperating scenario. Preventing such micro-welding and adhesive wear hasbeen shown to also improve the NVH performance of the differential. Inother examples, tip relief may be added in the involute profiledirection (measuring from root to tip). This further helps improve theload intensity plot in FIG. 14. Such tip relief may be produced withspecially designed hob cutters.

The foregoing description of the many examples has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular aspect are generally not limited to that particularexample, but, where applicable, are interchangeable and can be used in aselected example, even if not specifically shown or described. The samemay also be varied in many ways. Such variations are not to be regardedas a departure from the disclosure, and all such modifications areintended to be included within the scope of the disclosure.

What is claimed is:
 1. A parallel axis gear configuration comprising: afirst gear having a first gear tooth that includes a lead crowningacross a face width thereof, the lead crowning comprising: a first leadcrown defined from a centerline to a transition point; and a second leadcrown defined from the transition point to a first end point; andwherein the lead crowning includes a drop-off magnitude that is greaterat the second lead crown than the first lead crown.
 2. The parallel axisgear configuration of claim 1, further comprising a second gear that isin meshed relationship with the first gear.
 3. The parallel axis gearconfiguration of claim 2 wherein the first and second gears are helicalgears.
 4. The parallel axis gear configuration of claim 3, furthercomprising: a parallel axis differential that houses the first andsecond gears.
 5. The parallel axis gear configuration of claim 1 whereinthe first gear includes a chemical vapor deposit coating thereon.
 6. Aparallel axis gear configuration comprising: a first gear having a firstgear tooth that includes a lead crowning across a face width thereof,the lead crowning comprising: a first lead crown defined from acenterline to a transition point; and a second lead crown defined fromthe transition point to a first end point; and wherein the first andsecond lead crowns have a distinct magnitudes across the face width andwherein the first gear includes a chemical vapor deposit coatingthereon.
 7. The parallel axis gear of claim 6 wherein the second leadcrown includes a drop-off magnitude that is greater at the second leadcrown than the first lead crown.
 8. The parallel axis gear of claim 6wherein the first lead crown is zero.
 9. The parallel axis gearconfiguration of claim 6, further comprising a second gear that is inmeshed relationship with the first gear.
 10. The parallel axis gearconfiguration of claim 9 wherein the first and second gears are helicalgears.
 11. The parallel axis gear configuration of claim 7, furthercomprising: a parallel axis differential that houses the first andsecond gears.
 12. A parallel axis gear configuration comprising: a firstgear having a first gear tooth that includes a first gear tooth leadcrowning across a first face width thereof, the first gear tooth leadcrowning comprising: a first lead crown defined from a first centerlineto a first transition point; and a second lead crown defined from thefirst transition point to a first end point wherein the first gear toothlead crowning includes a first gear drop-off magnitude that is greaterat the second lead crown than the first lead crown; and a second gearhaving a second gear tooth that includes a second gear tooth leadcrowning across a second face width thereof, the second gear tooth leadcrowing comprising: a first lead crown defined from a second centerlineto a second transition point; and a second lead crown defined from thesecond transition point to a first end point wherein the second geartooth lead crowning includes a second gear drop-off magnitude that isgreater at the second lead crown than the first lead crown; and whereinthe first and second gears are received in a housing in a meshedrelationship.
 13. The parallel axis gear configuration of claim 12,wherein the housing comprises: a parallel axis differential that housesthe first and second gears.
 14. The parallel axis gear configuration ofclaim 12 wherein the first and second gears both include a chemicalvapor deposit coating thereon.
 15. The parallel axis gear configurationof claim 12 wherein the first and second gears are helical gears. 16.The parallel axis gear configuration of claim 12 wherein the first leadcrown of at least one of the first and second gear tooth lead crowningis non-zero.